Nitrogen-doped-carbon coated lithium iron phosphate cathode material with high performance for lithium-ion batteries

LiFePO4 coated with nitrogen-doped carbon (NC-LiFePO4) is successfully synthesized via a simple and efficient solid state method by using nitrogen-containing ionic liquid (IL) as nitrogen source. The uniformly coated N-doped carbon layers on the particles are examined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDS). The nitrogen-doped carbon layers on the particle surface can increase the electronic conductivity of LiFePO4, resulting in higher capacity and more superior rate capability compared with the one coated with undoped carbon (C-LiFePO4). The specific discharge capacities of NC-LiFePO4 are 160.1 mA h g−1 at 0.1 C and as high as 124.5 mA h g−1 at 10 C, while they are 149.1 mA h g−1 at 0.1 C and 95.7 mA h g−1 at 10 C for C-LiFePO4. The method reported in this paper is very effective in electronic conductivity improvement of LiFePO4 and can be easily applied to the synthesis of other cathode materials.